1. Field of Invention
The field of the present invention relates in general to communication systems and more particularly to pre-compensation systems for the transmit path of an XDSL modem.
2. Description of the Related Art
Digital Subscriber Lines (DSL) technology and improvements thereon including: G.Lite, ADSL, VDSL, HDSL all of which are broadly identified as X-DSL have been developed to increase the effective bandwidth of existing subscriber line connections. An X-DSL modem operates at frequencies higher than the voice band frequencies, thus an X-DSL modem may operate simultaneously with a voice band modem or a telephone conversation. Currently there are over ten discrete X-DSL standards, including: G.Lite, ADSL, VDSL, SDSL, MDSL, RADSL, HDSL, etc.
One of the factors limiting the bandwidth or channel capacity of any of the above discussed X-DSL protocols is distortion. The components on the transmit path of a modem inherently distort signals as they transmit them. Amplitude modulation causes distortion to become dependent on the input signal with a result of the amplified output signal is no longer simply an amplified replica of the input signal. Unfortunately if linear modulation with a fluctuating envelope is used in conjunction with nonlinear amplification, spectral spreading may occur thereby interfering with communications.
What is needed are approaches to reducing in band distortion for X-DSL modems.